Monophasic action potentials on epicardial and endocardial surface are conventionally recorded by using section electrodes, contact electrodes, and catheter technique. Those prior art can be seen respectively in articles of (1) "Einphasische Aktionsstrome vom in situ durchbluteten Saugetierzen," E. Schutz, Zeitschr Biol 92, pp. 441-452, 1932, (2) "The Monophasic Electrogram Obtained From The Mammalian Heart," K. Jochim et al, Am J Physiol 111, pp. 177-186, 1935, and (3) "Long-Term Recording Of Monophasic Action Potentials From Human Endocardium," M. R. Franz, Am J Cardiol 51, pp. 1629-34, 1983.
In 1992, the present inventor first introduced a needle electrode for recording intramyocardial monophasic action potentials. Such an electrode was described in an abstract of "A Method For Recording Of Intramyocardial Monophasic Action Potential In Intact Dogs: In Vivo Evidence Of M Cells," Y. G. Wang, R. J. Hariman, G. A. Gintant, et al, Pace Vol. 15 (part II), p. 559, April, 1992. Two rows of electrodes of the needle electrode are made of teflon-insulated fine chlorided silver wires. They are inserted into small holes placed along a 16 gauge sheath of a commercially available intravenous catheter (Angiocath). One row electrodes are made into ball-shape. The other row of electrodes are made by trimming the excess wires outside of the sheath. An 18 gauge needle (Abbocath) is used as a stylet inside the sheath to hold the electrodes in place.
However, the tips of both rows of electrodes are outside of the wall of the needle. Thus, they may cause two major problems when the needle electrode is inserted into the ventricular wall. First, the tips may injure the heart seriously. Second, the ball-type tips can be broken easily in the ventricular wall because the wires connecting the small ball tips are very thin. When the needle electrode is being inserted into the ventricular wall, the tips which are outside of the needle, will confront relatively big resistance so as to cause the connecting wires broken. These problems affect the accuracy of recorded data and certainly limit the use of the needle electrode in patients.
Another kind of needle electrode was used by Kasell and Gallagher in 1977 to record ventricular activation in animals and patients. See his article of "Construction Of A Multipolar Needle Electrode For Activation Study Of The Heart," Am J Physiol 233(2) H312-H317, 1977. However, it has only one row of electrodes on one side of the needle electrode. The electrodes are soldered in the wall of the needle. Such a needle electrode is not able to record monophasic action potential.
According to the principle of producing monophasic action potential, the following factors have to be considered in recording intramyocardial monophasic action potential. First, recording monophasic action potential needs bipolar electrodes. Second, the contact of the electrodes with the myocardial tissues must be different, i.e. one is fighter than the other, so that different injury potentials can be produced. Consequently, monophasic action potentials are produced. M. R. Franz describes this principle in his article of "Method and Theory of Monophasic Action Potential Recording," Progress in Cardiovascular Diseases, Vol. 33, No. 6, May/June, 1991, pp. 347-368. Third, it is important to note that, when the electrodes are being inserted into the ventricular wall, the myocardial tissues with which the electrodes contact, should not be seriously injured.